Crystallizing apparatus and method of operating the same



June 1964 K. EBNER 3, 37,544

CRYSTALLIZING APPARATUS AND METHOD OF OPERATING THE SAME Filed May 20,1958 2 Sheets-Sheet 1 lure/720m MRpEM [R f1 ga ATTORNEK June 16, 1964 K.EBNER 3,137,544

CRYSTALLIZING APPARATUS AND METHOD OF OPERATING THE SAME Filed May 20,1958 2 Sheets-Sheet 2 A ITdRWEKS' United States Patent 3,137,544CRYSTALLIZING APPARATUS AND METHOD OF ()PERATING THE SAME Karl Elmer,Oberursel, Taunus, Germany, assignor to MetallgesellschaftAktiengesellschaft, Frankfurt am Main, Germany, a corporation of GermanyFiled May 20, 1958, Ser. No. 736,618 6 Claims. (Cl. 23-273) Whencrystallizing solids from solutions, it is mostly desired to obtaincrystals which are as far as possible of uniform size and granular inform. If a salt-bearing liquid is cooled by evaporation under pressurewith the aid of a vacuum, a very fine grained crystal separates out onthe saturation point of the solution being considerably exceeded. Withina small range of temperature below the saturation point, a metastablestate prevails in which the crystalline growth takes place. Thetemperature range of this metastable state is not uniform in extent. Itgenerally becomes greater the higher the molecular weight of thedissolved substance is. The metastable range is considerably reduced byimpurities in the solution which cause increased and premature crystalnucleus formation.

If therefore it is desired to crystallize out a product as far aspossible in the form of uniform coarse grains from a solution cooledunder vacuum, it must be seen that a suflicient quantity of crystalswhich act as seeding crystals is present in suspension in the solutionin uniform distribution, but that the speed of nucleus formation alsoremains slow, so that the existing crystals and the crystal seeds cangrow to the desired grain size.

Therefore, it follows that the construction of the vacuum crystallizingapparatus should be such that the solution is preferably cooled instages, the reduction in temperature in each stage amounting, forexample, to 3 C. or 4 C. The crystals separating out become larger andmore uniform if the cooling in each stage is only about 1 C. In the caseof vacuum stages connected in series, however, a large number ofevaporators will be necessary resulting in a very expensive plant.

Vacuum crystallizing apparatus are known in which crystals can be grownby circulating a large quantity of liquid by means of a pump and onlycooling slightly in a vacuum, so that no crystals separate out but onlyslight oversaturation takes place. This oversaturated solution or aportion thereof is then passed through a layer of already formedcrystals mostly arranged outside the actual cooling apparatus, in whichlayer the existing newly formed crystals grow thereby reducing theoversaturation.

Evaporators with external heating systems have likewise been used forcrystallizing salts out of solutions. From the evaporator provided witha conical bottom the separated salts are drawn off through a sluice intoa centrifuge in which the liquid carried by the salt is centrifuged011?. Underneath a built-in unit of conical shape arranged in thecylindrical portion of the evaporator and connected at its upper edge tothe wall of the cylinder, cooled solution from the evaporator iscontinually drawn off and conducted into the heating element. It returnstherefrom re-heated, through a conduit which terminates just above theliquid level in the evaporator. The vapors forming in the evaporator arecondensed in a condenser. These evaporators are not suitable for crystalculture and the salt coming from the centrifuge contains a greatquantity of moisture.

According to another method of procedure, solution in the range ofmetastable saturation from a common evaporator was distributed toseveral crystallizers of different sizes, from which it was thenreturned into the evaporator.

The crystal growth took place due to the fact that a mixture of solutionand crystals was maintained in turbulent movement in each of thecrystallizers and that the crystals, on attaining a certain size,separated out of the solution under the action of the gyrating movement.They then passed into the next larger crystallizer in which they weredeveloped by the same system. Finally the crystals of the desired grainsize were drawn off from the largest crystallizer.

These circulating evaporators are, however, open to the objection thatthe relatively large pumps which operate against the vacuum arerelatively expensive apparatus.

The invention relates to crystallizing plants which are equipped with anevaporating zone and a crystallization zone and means by which thesolution from which uniform and coarse grained crystals are to beobtained, is maintained in circulation through the evaporating zone andthe crystallization zone. At the same time inlets and outlets areprovided by which the hot initial solution is introduced into the devicewith the conical bottom and by means of which the cooled solution, thevapors produced by self-evaporation and the separated crystals areconducted off from the crystallization process.

The invention consists in that funnel-shaped built-in units are providedin the evaporator vessel substantially concentric therewith. Thesebuilt-in units are arranged with clearance from the wall of theevaporating vessel. The apparatus according to the invention alsocomprises a conduit serving for guiding the circulation of the solution,which conduit first descends from the liquid level in the evaporatoroutside the evaporator and then rises so that its extremity is justabove the built-in units. The lowest point of the conduit is located 10to 20 times the height of lift of the liquid over the liquid level inthe evaporator below the level of the liquid in the evaporator and anair feed is arranged at the bottom of the conduit so that thecirculating motion of the solution through the conduit takes place onthe known air lift principle.

The units built-in the evaporator according to the invention which catchthe solution introduced into the evaporator, prevent the liquidscattered by self-evaporation from splashing the walls of the evaporatoras such splashes would quickly lead to the formation of large depositsand cause continual operating trouble. At the same time, owing to thefact that the circulation conduit for the solution according to theinvention first descends to a low level and then rises, the advantage isderived that very little air is used for the circulation of thesolution, so that the vapors produced during the evaporation can be usedfor heating purposes or, if the evaporation is carried out at lowtemperatures, these vapors can be condensed in standard condensers withthe usual air extracting devices. The combination of the evaporatingzone and the crystallizing zone in a vessel having a conical bottomenables very good crystal growth to be obtained, because the liquidwhich is guided by the built-in units from the circulation conduit rightinto the lower part of the evaporator, in rising in the conical bottommaintains the fine crystal grains in suspension until they grow intocrystals which can sink to the bottom against the flow of the liquid.

According to a special form of construction according to the invention,the growth of crystals when crystallizing salts or similar solidsubstances out of solutions maintained in circulation in known manner byvacuum evaporation and crystallization, is carried out in several stagesin such a manner that the solution is conducted successively through allthe stages and the freshly introduced solution is mixed with thesolution in circulation in each stage by vacuum evaporation andcrystallization. By mixing the 3 fresh solution introduced in each stagewith the solution in circulation a temperature is imparted to themixture composed of circulating liquid and fresh solution, which lieswithin the range of metastable saturation in the particular stage and,by the vacuum cooling of the liquid mixture, a portion of the heat isextracted which the freshly introduced solution has introduced and whichcorresponds to the drop in temperature between the two workingtemperatures of two successive stages.

Owing to the fact that the crystallization is carried out withcirculating liquid in this manner in several stages, the formation ofnew crystal nuclei during the cooling operation is prevented to a greatextent. It has been found that the formation of fresh seed in practiceis proportional to the quantity of liquid which is maintained incirculation during a unit of time. If the cooling in one or severalstages is to the limit of the available drop in temperature, arelatively large quantity of liquid must be kept in circulation so thatthe mixture composed of circulating liquid and freshly introduced liquidis brought within the range of metastable saturation. If, on the otherhand, the treatment in stages is carried out in such a manner that ineach stage the cooling is effected only to a fraction of the drop intemperature available, the necessary quantity of liquid circulating ineach stage is reduced in inverse proportion to the number of stages. Inthe case of three stages, only /3 and in the case of five stages only /5of the quantity of circulating liquid necessary for single stagecrystallization, is required. Now if the solution passes successivelythrough all the circulation stages, the seed crystals newly formed inthe preceding stage grow in the following stage and consequently alarger and more uniform grain is obtained than by the process in which,when also working in stages, the solution is cooled in each stage by thewhole of the drop in temperature available.

For example, if, according to the invention, the crystallization of thesalt or the like from the saturated or nearly saturated running solutionis carried out in three or four or even more stages, the temperature ofwhich drops by about 4 to 7 C., e.g. 5 C. from stage to stage in thedirection of liquid flow, before entering each stage the inflowingsolution entering the liquid circulation of the solution present in theparticular stage which is quantitatively measured so that the mixturecomposed of the hot freshly introduced solution andthe cold solution ofthe particular stage, assumes a temperature which is about 1 to 2 C.higher than the temperature of the liquid content in this stage. Themixture is introduced into the evaporating space of the particular stagewhere by partial evaporation its temperature is again reduced by 1 to 2C., that is, by the amount by which the temperature of the mixtureexceeds that of the stage. The liquid mixture is now passed into thisstage through an accumulation of salt in which the oversaturation of thesolution caused by the cooling is released in such a manner that thesalt crystals of the accumulation of salt grow. The accumulation ismaintained in suspension in such a manner that the grains of salt onlysettle when they have attained a certain size. The water vapor generatedin the stage is fed into the condensation by means of injectors, forexample into a common condenser, so as to keep the steam consumption ofthe plant as low as possible.

This embodiment of the invention possesses the further advantage thatthe steam consumption is far lower than in the known processes and thatapparatus can be used which is relatively inexpensive. The stages can beproduced by dividing a cylindrical vessel into chambers by radialpartition walls, through which chambers the solution to be treated isfed successively. The chambers can be so equipped with the aid ofconical bottom parts and funnelshaped built-in units from which thecirculating liquid is conducted by a pipe into the lower part of thechamber, so that a suitable quantity of salt is maintained in suspensionin the lower part in which the crystallization takes place. Heavy grainseparated out can, when it has attained at the desired size, becontinuously or periodically drawn off at the bottom of the chamber bymeans of known devices.

It has also been discovered that the crystal growth according to theinvention can be still further improved by conducting the liquid incirculation by means of gases which are introduced into the uptake ofthe liquid circulation. By this means, the apparatus necessary forcarrying out the method according to the invention, is simplified stillfurther; moreover the crystals produced retain their original shape,that is the edges and corners of the crystals are not rubbed off as isthe case, due to impact and friction, when other propelling devices suchas rotary pumps are used.

The invention is illustrated diagrammatically and by way of example inthe accompanying drawings, in which:

PEG. 1 is a vertical section through a single stage apparatus accordingto the invention;

FIG. 2 shows a multi-stage apparatus, also in vertical section, and FIG.3 is a section on line IIIIH of FIG. 2.

The apparatus illustrated in FIG. 1 comprises an evaporator 1 with vaporoutlet and vacuum connection 10, a discharge device 8 for removing theformed crystals, a

funnel-shaped built-in unit 5, 6 acting as guide surface and acirculating device 2. The evaporator 1 consists of a cylindrical upperpart and a lower part 3 conically tapering, if desired in steps, andwhich leads into the discharge sluice d for removing the crystals. Theevaporator is closed at its upper end by means of a cover 9 which ispreferably domed and in which the connection piece 10 for producing thevacuum and drawing off the vapors is arranged preferably centrally.

Thefunnelrshaped guide surface is preferably concentrically mounted inthe evaporator with its upper aperture higher than the liquid leveladjustable in the evaporator and with a pipe 6 extending from its loweraperture to within close proximity of the discharge sluice 8.

The circulating device consists of a pipe 2, the main portion of whichis bent in U-shape, one end of this pipe being bent out laterally andpassing through the wall of the evaporator. The mouth of this pipelength 7 which is located within the evaporator lies below the liquidlevel in the evaporator. The other end is bent over horizontally andpasses through the evaporator wall, terminating in a downwardly directedpipe section 11 over the centre of the funnel-shaped built-in unit 5.The mouth 12 of the pipe section 11 may be of nozzle shape.

' A throttle air admission inlet 4 is provided at the lower end of thelong arm of the U-shaped pipe. It may, for example, be so shaped thatthe pipe wall is provided with holes in its circumferential circle andthe pipe surrounded at this point with a sleeve or jacket 13 carrying apipe connection piece with throttle valve 14. An air feed pipe may bealso arranged in the jacket of the U-shaped pipe and provided on itsouter end with a throttle valve and at its inner end with one or morenozzles. The air feed may, however, also be efiected by means of a pipepassing through the wall of the U-shaped pipe and bent in the directionof flow in the interior of'the pipe. This, airadmission pipe is fittedwith a throttle valve on its end outside the pipe and with an outletnozzle on its inner end.

The solution to be crystallized is introduced into the short arm of theU-shaped pipe through a lateral connection piece 15. Excess mother lyeis removed from the evaporator vessel through the lateral connection 16,the inner end of which is located near the level of the liquid.

So as not to hamper the maintenance of the vacuum and to restrict as faras possible the dilution by air of the vapors generated during theevaporation, the quantity of air entering through the valve 14 should bekept at a minimum.

This is attained according to the invention by making the feed conduitas long as possible in relation to the lift. The lift is the distance itfrom the liquid level to the highest point of the feed conduit. Theliquid circulation which is attainable by a given quantity of air is somuch better the lower the air admission is below the liquid level. Thisdistance is designated by H on the draw ing. According to the inventionthe ratio h:H is taken at 1:10 to 1:20. The air before entering the ringconduit is preferably brought to saturation temperature corresponding tothe temperature of the circulated liquid.

The mouth of the circulation conduit is arranged so high above thefunnel-shaped built-in unit 5 that the liquid in the distributionexisting on this path is only cooled about 1 C.

The liquid reaches the narrowest zone of the conical lower part 3 of theevaporating vessel through the funnel 5 and the pipe 6 extendingtherefrom.

Owing to the suction effect at the commencement of the circulationconduit 2 an upward flow sets in in the vessel outside the funnel-shapedbuilt-in unit 5. The liquid passing out from the pipe 6 is thusdeflected upwards and then rises at a speed which becomes slower as thecross-section of the conical lower part of the Vessel 3 increases.

At the relatively high speed of flow in the neighborhood of the loweraperture of the pipe 6 crystals which have attained a minimum grain sizesettle. Smaller crystals are carried along by the current and, accordingto their size, are held in suspension in the zones of the largercross-section of the lower part of the vessel. They there grow to agrain size which enables their sedimentation.

The deposited crystals with uniformly well and regularly grown grainsize collect over the discharge 8 and form a bed of crystals from whicha portion is continually withdrawn by the discharging device mixed withas much mother lye as is advantageous for the subsequent separation ofthe crystals in a centrifuge.

In the conical lower part of the vessel a sedimentation zone forms abovethe bed of crystals and is followed by a clearing or settling zone inthe cylindrical part of the vessel. The solution entering thecirculation is generally clear and practically free from crystals.

The sedimentation zone in the lower part of the vessel may, as shown inthe drawing, be constructed with another conically tapering part as thepart directly adjoining the cylindrical wall. If this conical lower partis made slimmer, speeds diminishing more slowly along a longer path willbe obtained than with a cone which is not so steep. As a result thecrystals remain in suspension along a longer path of travel in theslimmer lower part. Therefore it is possible to allow the oversaturatedlye to act for a longer or shorter period on the crystals held insuspension. In the case of saline solutions which have a lesser tendencyto oversaturation it is therefore possible to keep the sedimentationzone small and in the case of saline solutions with a high degree ofoversaturation to make this zone longer.

As, however, the circulation takes place without pulsation and suddendeflections, such as always occur when using rotary pumps, it is of nosignificance if smaller crystals also enter the circulation conduit.

To avoid deposits of crystals within the apparatus, which would finallyresult in the formation of turbulent flow, the funnel-shaped built-in 5,6, the discharge sluice 8 and the pipe length 7 of the circulatingconduit 2 located within the vessel, can be made of soft rubber.

Mother lye is drawn off continually or periodically through thedischarge 16 in order to avoid the concentration of impurities in thesolution in circulation. This drawn olf lye can, preferably afterundergoing an intermediate treatment in a cyclone separator or the like,be again further concentrated and crystallized in one or severalcrystallizing apparatus according to the invention.

The apparatus illustrated in FIGS. 2 and 3 consists of a cylindricalwall 21 which is divided, for example, into four chambers by partitionwalls 22 and 23. Each of these chambers accommodates a funnel-shapedbuilt-in unit with a cylindrical extension projecting into the funnel-shaped lower part of the chamber.

The solution from which the salt or other solid substances are to becrystallized out, is passed successively through all the chambers and ineach chamber is cooled by partial evaporation under vacuum. For example,the solution passes in saturated or nearly saturated state through theconduit 26 into the liquid circulation in the conduits 27, 28. Liquidhaving a temperature corresponding to that of the vacuum prevailinginthe chamber a flows through the conduit 27 in downward direction outof the chamber a. It returns, mixed with the warmer solution fed throughthe conduit 26, via the conduit 28 into the chamber a dropping into thefunnel-shaped built-in unit 24. The quantity of liquid led off from thechamber a through the conduit 27 amounts to a multiple of the quantityof the liquid flowing in at 26. It is so calculated that the mixturecomposed of cold circulating liquid and the warmer freshly arrivedliquid is given a temperature which is higher by about 1 to 2 C. thanthe temperature maintained by the vacuum evaporation in the liquidcontent of the chamber a. On entering the chamber'a the liquid is againcooled about 1 to 2 C. to the temperature of the liquid in this chamber.During the cooling process no salt crystals sepa rate out. The crsytalsfirst form in the lower funnelshaped part of the chamber a into whichthe solution flowing out' at 28 oversaturated by cooling, passes throughthe cylindrical extension 25. When the crystals have attained asufliciently large size they settle in the part 29 of the chamber a andcan be withdrawn continually or periodically, for example, through athrottle element 30. The vacuum in the chamber a is produced by a steamjet apparatus 31 which feeds into a steam condenser (not shown). Thecirculation of the liquids through the conduits 27 and 28 is effectedwith the aid of known conveying arrangements, for example, by means of asmall quantity of air which is introduced into the conduit 28 through aring-shaped nozzle 32.

From the chamber a the liquid which has cooled therein through partevaporation in a vacuum to a temperature which is, for example, 5 C.lower than that of the liquid arriving through 26, passes through theconduit 33 into the liquid circulation 34, 36 of the next chamber bwhich is maintained in the same way as the liquid circulation throughthe conduits 27 and 28 coordinated to the chamber a, by known conveyingarrangements such as the introduction of air by means of a device,preferably a ring nozzle 35. The liquid circulation and the guiding of'the liquid into and through the chamber b are carried out in the sameway as in the case of chamber a, in that the liquid coming out of theconduit 33 cooled to a temperature about 1 to 2 C. above the temperatureprevailing in the chamber b by mixing with a many times greater quantityof liquid flowing through the conduit 34, drops through 36 into thefunnel 37 and is guided downwards by the cylindrical extension 38thereof into the conical part of the chamber 11 where the crystallizingout from the liquid cooled by about 1 to 2 C. on entering the chamber12, takes place. The large crystals obtained by this crystal growth inchamber 39 can be led off through a throttle element 40 wihch can beconstructed and operated, for example, in a similar manner to thethrottle element 30 in the chamber a. The vacuum is produced in thechamber b by steam jet apparatus 41 which, just like the steam jet 31,conducts the steam to a steam condenser (not shown). The liquid passingout of the chamber b is led off through the conduit 42 to be furthertreated in the chambers c and d in the same way as in the chambers a andb, these chambers c and d being equipped with built-in units, operatedand evacuated by steam jet apparatus into steam condensers, just as inthe case of the chambers a and b. From the last chamber d-there tus atthe desired final temperature.

can also be more than four chambers connected in seriesthe liquid passesout of the crystallizing apparalBy cooling in stages in theseries-connected chambers a, b, c, d a particularly uniform crystalgrain is obtained. The steam consumption of the jet apparatus eliectingthe cooling, is also low because these have to overcome a considerablysmaller drop in temperature than in the known crystallizers. If theseries-connected chambers are formed by dividing a cylindrical space bypartition walls, the partition walls can be thin because the dillerencein pressure between the individual stages is slight. The chambers arepreferably insulated from each other, which can be effected, forexample, by making the partitions 22, 23 double walled when the spacebetween the Walls is either filled with heat insulating substances ormaintained under a good vacuum. By the heat insulation of the chambersfrom one another, deposits of crystal on the partition walls areprevented.

Example 1 From a sodium sulphate solution with 23% Na so, and H 80 300g. of Glaubers salt per litre of the solution were to be obtained incoarse crystalline form. The equipment illustrated in FIG. 1 of thedrawing was used for the crystallization. The solution to be treated wasintroduced at at a temperature of 15 0., mixed in flowing through thepipes 2 and 11 with the circulating solution flowing out of the vessel 1at 7 an passed out at 12 at a temperature of 13 C. The solution in theevaporator had a temperature of 10 C. The precipitated salt was led oilfrom the crystallizing evaporator with a quantity of the solution andfed into a centrifuge. It left the centrifuge with a moisture content ofonly 3%. The evaporator was operated under avacuum of 6.5 torr. With adiameter of 1.6 m. and a cylindrical height of 2 m. it produced about1000 kgs. Glaubers salt per hour. The vapors which left the evaporatorthrough the vapor discharge 10 had such a small air content that thecoudenser (not shown) in which the vapors were condensed, could beoperated with ordinary ventilation and supplementary means were notrequired for eliminating the transporting air introduced at the bottomof conduit 11.

Example 2 A potassium chloride solution saturated at 95 C. was cooled to45 C. in a crystallizing apparatus according to the invention. In theapparatus 2.5 in. in diameter operating with a solution flow of 15 cb.in. per hour, about 1300 kgs. of salt were obtained per hour with agrain Percent Exceeding 0.5 mm About 90 Between 0.2 and 0.5 mm About 5to 7 Less than 0.2 mm About 3 to 5 The salt was in the lower part of thecrystallizer according to the invention in loose state and could easilybe removed without choking. On the other hand in a known 24-stage vacuumcooling plant a crystallate grain was obtained of which About 9%exceeded 0.5 mm., About 69% was between 0.2 and 0.5 mm., and About 22%less than 0.2 mm.

Example 3 A potassium chloride solution saturated at about 90 C. wascooled in one stage in a crystallizer which was equipped with liquidcirculation. From this circulation lye was extracted at the bottom ofthe crystallizing vessel and fed onto the surface of the liquid in thecrystallizing vessel by air which was introduced into the uptake of thecirculation conduit. The flow of lye amounted to 15 ch.

m./hr.; whereby potassium chloride, partly also sodium chloride,crystallized out with the following sieve analysis:

Percent Exceeding 1 mm "7 From 0.75 to 1 mm 5 From 0.2 to 0.75 mm 73Less than 0.2 mm 15 The same solution was worked in two stages at in allthe same temperature range and the drop of temperature according to theinvention maintained in the stages; as a result, from the same solutionwith the same lye flow a crystal grain of the following grain sizes wasobtained:

Percent Exceeding 1 mm 10 From 0.75 to 1 mm 20 From 0.2 to 0.75 mm n 60Less than 0.2 mm 10 defining a funnel-shaped chamber being open at bothits upper and lower ends completely disposed within said vessel andspaced from the sides thereof at both said upper and lower ends, theupper end of said funuel-shaped chamber extending into said evaporationzone andsthe lower end of said funnel-shaped chamber extending into saidcrystallization zone, said vessel being capable of containing a solutionat a level at least below the upper end of said funnel-shaped chamber,means for removing vapors from the'top of said vessel, circulating meansfor withdrawing solution from said vessel to a lower level and thence toan upper level and terminating in a discharge opening above and spacedfrom said funnel-shaped chamber, said lower level being below the levelof said solution a distance of from about 10 to 20 times the distancesaid upper level is above the level of said solution, an air inlet meansconnected to said circulating means at said lower level, and means foradding fresh solution to said apparatus.

2. An apparatus for obtaining large and uniform crystals from solutionswhich comprises a closed vessel having an inwardly and downwardlytapering bottom portion, said bottom portion terminating in a crystaldischarge outlet, said vessel being divided into an upper evaporationzone and a lower crystallization zone, means defining a funnel-shapedchamber being open at both its upper and lower ends completely disposedwithin said vessel and spaced from the sides thereof at both said upperand lower ends, the upper end of said funnel-shaped chamber extendinginto said evaporation zone and the lower end of said funnel-shapedchamber extending into said crystallization zone, said vessel beingcapable of containing a solution at a level at least below the upperendof said funnel-shaped chamber, means for removing vapors from the top ofsaid vessel, means for removing excess solution from saidvessel,'circulating means including inlet means disposed within saidvessel below the level of said solution for withdrawing solution fromthe upper portion of the crystallizing zone of said vessel, exteriorconduit means for passing said solution first to a lower level andthence to an upper level and outlet means disposed directly above andspaced from said upper end of said funnel-shaped chamber for dischargingsaid solution thereinto, said lower level being below the level of saidsolution a distance of from 10 to 20 times the distance said 7 upperlevel is above the level of said solution, an adjustable air inlet meansconnected to said conduit means at said lower level, and means foradding fresh solution to said conduit means.

3. An apparatus according to claim 1 wherein the bottom portion of saidclosed vessel tapers inwardly and downwardly in stages to definecorresponding settling zones.

4. An apparatus according to claim 1 wherein a plurality of said vesselsare arranged in series, said apparatus having conduit means for passingsolution from each vessel to the next subsequent vessel.

5. An apparatus for obtaining large and uniform crystals from solutionswhich comprises a plurality of closed vessels each having an inwardlyand downwardly tapering bottom portion, each said bottom portionterminating in a crystal discharge outlet, said vessels being dividedinto an upper evaporation zone and a lower crystallization zone, meansdefining a funnel-shaped chamber being open at both its upper and lowerends completely disposed within each said vessel and spaced from thesides thereof at both said upper and lower ends, the upper end of saidfunnel-shaped chambers extending into the corresponding evaporation zoneand the lower end of each said funnelshaped chamber extending into thecorresponding crystallization zone, each said vessel being capable ofcontaining a solution at a level at least below the upper end of thecorresponding funnel-shaped chamber, means for removing vapors from thetop of each said vessel, circulating means for withdrawing solution fromeach said vessel to a lower level and thence to an upper level andterminating in a discharge opening above and spaced from thecorresponding funnel-shaped chamber, each said lower level being belowthe level of said solution a distance of from about 10 to 20 times thedistance each said upper level is above the level of the correspondingsolution, an air inlet means connected to each said conduit means atsaid lower level, and means for conducting solution from the upperportions of the crystallizing zone of each said vessel to thecirculating means of the next.

6. In an apparatus for obtaining large and uniform crystals fromsupersaturated solutions capable of yielding such crystals, including aclosed vessel having an inwardly and downwardly tapering bottom portionterminating in a crystal discharge outlet and being divided into anupper evaporation zone and a lower crystallization zone, means forremoving vapors from the top of said vessel and means for adding freshsolution to, for removing excess solution from and for circulating atleast a 10 portion of the solution by withdrawing said solution from andreturning the same to said vessel, the improvement which comprisesproviding completely disposed within said closed vessel means defining afunnel-shaped chamber open at both its upper and lower ends and spacedfrom the sides thereof at both said upper and lower ends, the upper endof said funnel-shaped chamber extending into said upper evaporation zoneand the lower end of said funnel-shaped chamber extending into saidlower crystallization zone, said vessel being capable of containing asolution at a level at least below the upper end of said funnehshapedchamber, said means for circulating including inlet means thereforedisposed within said vessel below the level of said solution forwithdrawing solution from the upper portion of the crystallization zoneof said vessel, exterior conduit means for passing said solution firstto a lower level and thence to an upper level, outlet means disposeddirectly above and spaced from said upper end of said funnel-shapedchamber for discharging said solution downwardly thereinto, said lowerlevel being below the level of said solution a distance of from 10 to 20times the distance said upper level is above the level of said solutionand an adjustable air inlet means connected to said exterior conduitmeans at said lower level.

References Cited in the file of this patent UNITED STATES PATENTS1,099,396 Rothwell June 9, 1914 1,550,521 Du Faur Aug. 18, 19251,945,281 Leith'aiuser Jan. 30, 1934 2,042,661 Jeremiassen June 2, 19362,219,776 Henderson Oct. 29, 1940 2,375,922 Jeremiassen May 15, 19452,567,968 Saeman Sept. 18, 1951 2,631,926 Eckstrom Mar. 17, 19532,737,451 Saeman Mar. 6, 1956 2,827,366 Saeman Mar. 18, 1958 2,856,270Saeman Oct. 14, 1958 2,883,273 Saeman Apr. 21, 1959 FOREIGN PATENTS503,594 Germany July 24, 1930 399,250 Italy Oct. 21, 1942 924,027Germany Feb. 24, 1955 OTHER REFERENCES Perry: Chemical Eng. Handbook,page 1438, 3rd edition, 1949.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No., 3 137544 June 16V 1964\ KarlEbner It is hereby certified that error appearsin the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 7 line 29,, for "an" read and column 9 line 36 for "conduit" readcirculating line 38 for portions" read portion column l0, line l3, for"therefore" read therefor Signed and sealed this 27th day of October1964 (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. AN APPARATUS FOR OBTAINING LARGE AND UNIFORM CRYSTALS FROM SOLUTIONS WHICH COMPRISES A CLOSED VESSEL HAVING AN INWARDLY AND DOWNWARDLY TAPERING BOTTOM PORTION, SAID BOTTOM PORTION TERMINATING IN A CRYSTAL DISCHARGE OUTLET, SAID VESSEL BEING DIVIDED INTO AN UPPER EVAPORATION ZONE AND A LOWER CRYSTALLIZATION ZONE, MEANS DEFINING A FUNNEL-SHAPED CHAMBER BEING OPEN AT BOTH ITS UPPER AND LOWER ENDS COMPLETELY DISPOSED WITHIN SAID VESSEL AND SPACED FROM THE SIDES THEREOF AT BOTH SAID UPPER AND LOWER ENDS, THE UPPER END OF SID FUNNEL-SHAPED CHAMBER EXTENDING INTO SAID EVAPORATION ZONE AND THE LOWER END OF SAID FUNNEL-SHAPED CHAMBER EXTENDING INTO SAID CRYSTALLIZATION ZONE,SAID VESSEL BEING CAPABLE OF CONTAINING A SOLUTION AT A LEVEL AT LEAST BELOW THE UPPER END OF SAID FUNNEL-SHAPED CHAMBER, MEANS FOR REMOVING VAPORS FROM THE TOP OF SAID VESSEL, CIRCULATING MEANS FOR WITHDRAWING SOLUTION FROM SAID VESSEL TO A LOWER LEVEL AND THENCE TO ANUPPER LEVEL AND TERMINATING IN A DISCHARGE OPENING ABOVE AND SPACED FROM SAID FUNNEL-SHAPED CHAMBER, SAID LOWER LEVEL BEING BELOW THE LEVEL OF SAID SOLUTION A DISTANCE OF FROM ABOUT 10 TO 20 TIME THE DISTANCE SAID UPPER LEVEL IS ABOVE THE LEVEL OF SAID SOLUTION, AN AIR INLET MEANS CONNECTED TO SAID CIRCULATING MEANS AT SAID LOWER LEVEL, AND MEANS FOR ADDING FRESH SOLUTION TO SAID APPARATUS. 